1 files changed, 1 insertions, 1 deletions
diff --git a/cpp/src/IceGrid/ServerI.cpp b/cpp/src/IceGrid/ServerI.cpp
index 2e0910420e2..81a85c97157 100644
--- a/cpp/src/IceGrid/ServerI.cpp
+++ b/cpp/src/IceGrid/ServerI.cpp
@@ -320,7 +320,7 @@ struct EnvironmentEval : std::unary_function<string, string>
             else
             {
                 end = beg + 1;
-                while((isalnum(v[end]) || v[end] == '_')  && end < v.size())
+                while((isalnum(static_cast<unsigned char>(v[end])) || v[end] == '_')  && end < v.size())
                 {
                     ++end;
                 }